In telecommunication equipment designed to receive incoming signals, especially those of the binary type, it is frequently desirable to stabilize the signal level at a predetermined value. Thus, an incoming signal of magnitude S should be multiplied by a level-controlling modifier X.sub.o =R/S where R is a fixed reference value representing the desired signal amplitude. A direct establishment of modifier X.sub.o, however, is difficult since it would require continuous division of the fixed reference level R by the variable magnitude S.
Theoretically, the variable modifier X.sub.o could also be determined through successive approximations by the use of an iterative algorithm such as one designed to minimize the squared error (X-X.sub.o).sup.2 where X is an instant value approaching X.sub.o. The value X.sub.n of parameter X at an instant t.sub.n can be derived from an earlier value X.sub.n-1 (obtained at a preceding instant) from the relationship EQU X.sub.n =X.sub.n-1 -.beta..DELTA. (1)
where .beta. is a fractional constant designed to insure a stable feedback while .DELTA. is the gradient of the squared error, being thus given by 2(X-X.sub.o). Thus, equation (1) can be rewritten as follows: EQU X.sub.n =X.sub.n-1 -2.beta./S.multidot.(S.multidot.X.sub.n-1 -R)(2)
with X.sub.n-1 substituted for X in the foregoing expression for .DELTA.. This gradient algorithm has the advantages of simplicity and speed of convergence; however, the need for division by the variable signal level S would again create considerable circuital problems.
A prior solution to this problem resides in the provision of a read-only memory (see, for example, Italian Pat. No. 980,804) storing different values for the quotient R/S in as many cells addressable by the incoming signal. Evidently, such a memory must have a large storage capacity if a substantial number of signal levels are to be accommodated.